Kappa Concentration per Cell in Relation to the Life Cycle, Genotype and Mating Type in Paramecium Aurelia , Variety 4

Abstract

Exptl. animals were grown in depression slide cultures at 27[degree]C, with daily isolations to maintain a max. fission rate (5 fissions per day). The animals were kept in sterile culture fluid for 1 1/2 hrs. before fixation in order to free them of food vacuoles and facilitate kappa counts. They were isolated into the sterile fluid 3 hrs. after each of the 1st 3 post-fertilization fissions and at 5-hr, intervals thereafter, so that a standard stage of the fission cycle might be obtained. Animals were fixed with Schaudinn''s fixative and stained with a modification of DeLamater''s basic fuchsin technique. Counts of kappa particles were made at a magnification of 900x, using a glass grid in the ocular. Two cultures of variety 4 were used, killer stock 51 carrying K and a sensitive strain dl86 carrying k. Variations in kappa concn. during the life cycle of an animal were detd. for genotypes KK and Kk of both mating types, VII and VIII. For the 4 kinds of cultures kappa concn. per cell differed during 3 stages of the life cycle. The amt. of kappa increases during the 1st stage, from soon after fertilization until the 2nd fission, decreases to the pre-fertilization level from the 3rd to the 7th fissions, and remains constant from the 8th to the 14th fissions. At each stage, within each mating type, the homo-zygotes had about twice as much kappa as the heterozygotes, whereas for each genotype, type VII cells had about twice as much kappa as type VIII cells. Repetitions of tests during the 3rd stage of the life cycle gave average kappa concns. of 200 particles per cell for Kk type VIII, 400 for KK type VIII and Kk type VII, and 800 for KK type VII. When mating type VIII underwent a change to mating type VII, the kappa count also changed from 327 for type VIII to 678 for type VII. A change in genotype was made by allowing Kk killers to undergo autogamy and observing the resulting KK and kk clones for the 1st 15 fissions. The 2 clones could not be distinguished by kappa counts before the 8th fission. At the 9th fission the KK genotype showed a sudden mean increase in kappa concn. of 116 particles, with the higher rate being maintained at succeeding fissions. In the KK clones loss of kappa in individual cells was as sudden as its rise in KK cells, but did not occur in all cells at the same fission, so that kappa was not completely lost until the 15th fission. It was calculated that kappa in a kk exautogamous animal increased to an amt. 210 to 211 times that initially present before kappa completely disappeared, possibly due to fragments of the previous Kk macronucleus.